Space engineers are excited by the prospect of designing and sending tiny ‘cubesats' into orbit — small-scale satellites that are cheap to build, easy to put into space, and can perform highly specialized tasks like clearing out space junk. The problem, however, has been in figuring out a way to reposition these devices once they're in orbit. But a recent breakthrough by MIT's Paulo Lozano now suggests that cubesats may be given mobility by equipping them with mini ion thrusters.

The MIT team led by associate professor of aeronautics and astronautics Paulo Lozano is tackling this problem with the development of a rocket thruster that's about the size and shape of a sugar cube. Its upper face is made up of 500 microscopic tips, each a tiny thruster in its own right. The purpose of this thruster is to greatly simplify the design and hence save space and weight. Whether burning fuel or using cold gas, conventional thrusters need valves, tanks, pipes, venturis and other components that take up weight and space. The MIT microthrusters are not only smaller, they're mechanically very simple, yet technologically very sophisticated.

Each thruster is made of a reservoir of fuel at the bottom of the cube that Lozano describes as a "‘liquid plasma' of free-floating ions." Above this reservoir are layers of porous metal. Each pore leads into more numerous, smaller pores on the next level like the spreading branches of a tree. By the time they reach the top layer, there are 500 pores that make up the thruster tips. On the very top is a perforated gold plate, which acts as a cathode. When the plate is electrified, it charges the fuel drops in the thruster tips, turning them into charged ions and expelling them at high speed to generate thrust. In essence, the thruster is a tiny ion drive.

The clever bit about this whole arrangement is that the ions shooting out of the thruster generate a capillary effect in the system of pores. Like sap being drawn up a tree, the capillary pressure draws the fuel to the thruster tips without any mechanical pumps or valves.

Lozano was able to test his ion thrusters by mounting them on a mockup satellite that was suspended in space with counterbalanced magnetics. The entire apparatus was then placed in a vacuum chamber to mimic the conditions of space itself. Their experiment showed that the microthrusters were capable of exerting about 50 micronewtons (0.037 ft-lbs) — all that's required to move such a tiny satellite in freefall orbit.